Modelling the Optical Properties of Soot Particles under Various Aging Conditions

Kangwei Li,Wen Yang,Jiandong Shen,Chunmei Geng,Merched Azzi,Mingming Yan,Xin Zhang

doi:10.3390/atmos11010086

Abstract

As atmospheric fresh soot particles age, they become coated with other chemical species. This transforms their physicochemical properties and affects their optical characteristics, which is of great importance to air quality, the environment and climate change. One of the predominantly occurring states of soot particles in the ambient environment is the core-shell mixing state. In this study, we used the core-shell model to calculate the optical absorption, scattering and extinction efficiency, absorption proportion and absorption exponent of coated soot particles. We then investigated the effects of different core sizes (D0), incident wavelengths (λ), coating materials and coating thicknesses on these optical characteristics. Absorption efficiency and absorption proportion of soot particles decreased as the coating became thicker, at core sizes of D0 = 20, 50 and 100 nm and λ = 405, 532 and 781 nm, regardless of the type of coating material. As the coating thickness increased, the absorption exponent (β) of inorganic-coated soot particles tended to rise and then fall, while the β value of organic-coated soot particles kept increasing. Our results advance our scientific understanding of the interaction of optical properties with chemical composition, mixing state, and aging processes of soot particles in the atmosphere.

Highlights

Fresh soot particles can be as seed particles in the atmospheric aging process, where these secondary species from complex photochemical reactions with volatile organic compounds (VOCs), SO2, and NOx can be coated onto soot particles depending on the aging conditions [1,2]
Measured the optical properties of atmospheric particles in Xi’an. They showed that the fraction of coated organic compounds onto soot particles increased significantly during heavily polluted periods, and that light absorption at 870 nm increased almost three times due to the coatings of internal mixed soot particles [6]. These studies indicate that coating materials can change the optical properties of soot particles during the chemical aging process and increase their light absorption at different wavelengths compared with fresh soot particles
We investigated the variation in absorption efficiency (Qabs ), scattering efficiency selected for model calculation

Summary

Introduction

Fresh soot particles can be as seed particles in the atmospheric aging process, where these secondary species from complex photochemical reactions with volatile organic compounds (VOCs), SO2 , and NOx can be coated onto soot particles depending on the aging conditions [1,2]. Measured the optical properties of atmospheric particles in Xi’an They showed that the fraction of coated organic compounds onto soot particles increased significantly during heavily polluted periods, and that light absorption at 870 nm increased almost three times due to the coatings of internal mixed soot particles [6]. These studies indicate that coating materials can change the optical properties of soot particles during the chemical aging process and increase their light absorption at different wavelengths compared with fresh soot particles

Methods

Results

Conclusion